1. Field of the Invention
The present invention relates to an interactive multiaxis encoder system capable of accurately positioning a tool or a support platform. More particularly, the present invention relates to a novel encoder system which enhances the positioning accuracy of manufacturered guides, slides and bearing systems for mechanically positioning tools and support platforms.
2. Description of the Prior Art
Heretofore systems which could be designated as multiaxis positioning systems were not interactive. Prior art positioning systems employed encoders with scales which were sensed by encoders to determine the direction of movement of a single axis. As an example, prior art X-Y tables used in the semiconductor industry are positioning in the X direction by sensing signals from the X direction encoder-sensor. If the movement of the table or platform along the X axis is not perfectly parallel to the theoretical X axis, there is a slight angular diversion which includes an increment Y axis movement. The prior art Y axis encoder-sensors are incapable of sensing this incremental Y axis error. Thus, for purposes of this invention the term interactive and multiaxis refers to the ability to sense movement in the X or Y direction when the positioning encoder system is moving in the orthogonal direction.
Manufacturers of X-Y tables were and still are being requested by consumers and users of X-Y tables to provide greater accuracy of orthogonality and movement. The prior art response has been to manufacture more accurate and more expensive guides, slides, bearings, encoders, sensors and scales not realizing that a part of the problem is that the machine guides and mechanical components of these mechanical systems changed their dimensions and tolerances when incorporated into a positioning system and are placed in use under strained conditions. Changes in the stress of the moving parts or in the temperature of the moving parts and the differential temperature of the moving parts as well as changes in friction, lubrication and contamination all affect the accuracy of movement of X-Y tables and other types of positioning apparatus.
It is possible to make semiconductor masks for use in manufacturing semiconductors with defined lines having a width of less than one micron. To achieve such small accurate widths it is necessary to align a large number of such mask over the same line during different process steps, thus, it is desirable to repeatedly achieve positioning accuracies in the order of 1/100th of a micron which is straining the ability of the manufacturers positioning equipment to produce such equipment at any price.
It would be extremely desirable to provide a multiaxis positioning system which is extremely accurate and cheap to manufacture which would permit positioning accuracy independent of the accuracy of the mechanical guides, slides and bearings of the positioning system.